PROJECT SUMMARY Diabetes mellitus is a group of metabolic disorders characterized by high blood sugar, which is caused by deficiencies in insulin secretion and/or insulin action. Chronic diabetes can result in complications such as heart and peripheral vascular disease, kidney failure, limb amputation, and blindness and can even contribute to carcinogenesis. Diabetes represents a significant health and economic concern in the US: Nearly half of the US population is either diabetic or pre-diabetic, and the estimated economic burden of diabetes in the US in 2017 was over $300 billion, including $237 billion in direct medical costs and $90 billion in lost productivity. Most patients with diabetes have Type 2 diabetes (T2D), which typically begins with insulin resistance. Estrogen (E2) is known to protect against the development of diabetes, but is not a preferred treatment, especially in men and in post-menopausal women. The actions of E2 are widely assumed to occur through the classical nuclear estrogen receptors (ERs). However, recent studies have implicated the involvement of a novel G protein-coupled estrogen receptor (GPER), distinct from the classical ERs. GPER and its selective agonist G-1 mediate only a subset of the actions of E2 in vitro and in vivo, and in particular do not activate classical ER/ERE-mediated transcriptional activity (largely responsible for the feminizing effects of E2). Thus, GPER-selective activation via G-1 represents an innovative approach to the treatment of T2D, particularly in post-menopausal women as well as in men. In addition to stimulating insulin secretion, GPER activation limits ?-cell apoptosis and may reduce or even reverse insulin resistance in peripheral tissues. G-1 therefore has the potential to act as a multi-pronged approach to the treatment of T2D. GPER G-1 Development Group intends to develop the GPER agonist G-1 as a novel diabetes treatment based on the documented beneficial effects of E2 on disease progression and severity. In this Phase I STTR project, racemic G-1 will be resolved into its enantiomers and the active enantiomer determined in vivo (Aim 1). Next, for the active enantiomer, the in vitro toxicity will be assessed via AMES mutagenicity and hERG assays, and the in vivo toxicity and pharmacokinetics of G-1 will be examined using acute dose-escalation and repeat dose-range finding toxicology studies in male and female Sprague Dawley rats (Aim 2). This Phase I work will lay the foundation for more extensive, IND-enabling studies in Phase II.